1. Field of the Invention
The present invention relates to a golf club head and more particularly to a structure and method for fastening a weight in a metal-wood golf club head.
2. Prior Art
Among golf clubs, those called xe2x80x9cwoodsxe2x80x9d are required to contribute to increase the traveling distance of a struck golf ball. Therefore, the overall weight of recent clubs has been reduced by forming the club head from a light metal such as titanium, etc., and the weight body consisting of a metal with a large specific gravity is embedded inside the club head in order to increase the moment of inertia.
In one method to attach such a weight body to the club head, an externally-threaded screw is formed on the outer circumferential surface of a weight body and an internally-threaded screw hole is formed in the ground-contacting surface of the club head, i.e., in the sole plate of the club; and the weight body is screwed to the club head. In another method, a weight body is accommodated in a recess formed in the sole plate of the club head and fastened in place by an adhesive, etc.
However, in the above screw-engagement structure, a slight gap is unavoidably generated between the sole plate and the weight body for structural reasons. As a result, the style of the club in terms of external appearance is not always favorable. Furthermore, as the club is repeatedly used, the weight body may shift in position or drop out of the club head as the screw is loosened. Accordingly, such clubs lack stability in terms of product precision. On the other hand, in the above-described bonding structure of the weight body to the club head, a slight gap is also inevitable between the sole plate and the weight body. In addition, in such an adhesive bonding structure, the fastening strength drops as a result of deterioration of the adhesive agent over time, etc. Thus a weight body with a mass that effectively increases the moment of inertia cannot be employed.
Japanese Patent Application Laid-Open (Kokai) No. H10-94632 discloses a structure in which a weight body consisting of a different material from the sole plate is fastened to the sole plate. The weight body is welded to the sole plate via a spacer that is made of the same metal as the sole plate. However, in this weight body fastening structure, it is necessary to first wrap a band-form spacer around the outer circumferential surface of the weight body so as to fasten the spacer to the weight body, then to press-fit the weight body on which the spacer has been mounted in a seating part (accommodating section) formed in the sole plate, and further to fasten the spacer and sole plate to each other by welding.
In other words, in this fastening structure disclosed in the Japanese Laid-Opened Patent Application, though the spacer and the weight body are engaged, the strength of such an engagement of the spacer and the sole plate depends on welding. Accordingly, it is necessary to perform a separate welding process when the weight body is fastened to the sole plate. Thus, the work of fastening the weight body to the sole plate requires extra steps, hindering an easy mounting of the weight body to the club head. Furthermore, in the above method, the welding precision plays an important role in the precision of the final product; accordingly, the work requires extreme skill. In addition, a long manufacturing time is required, the productivity tends to be low, and these problems are inevitably reflected in the cost of the product.
Accordingly, the main object of the present invention is to solve the above-described problems in the prior art golf club head.
Another object of the present invention is to provide a fastening structure and fastening method of a weight body in a golf club head which allows easy mounting of the weight body to the club head and accomplishes firm fastening of the weight body to the club head.
Still another object of the present invention is to provide a fasting structure and fastening method of a weight body in a golf club head which improves the style of a golf club head in terms of the external appearance of the golf club head.
In order to accomplish the above-described objects, in the present invention, a first engaging part is formed in an accommodating section formed in a golf club head and a second engaging part is formed in a weight body that is to be installed in the club head; and a spacer is forcibly engaged with such first and second engaging parts when the weight body is press-fitted into the accommodating section with the spacer in between, so that the spacer expands and securely holds the weight body in the golf club head.
With the structure above, there is no need to perform any fastening work such as welding, etc.; and the weight body can easily be mounted in the accommodating section of the club head. Furthermore, not only is the weight body press-fitted inside the accommodating section, but the spacer also forcibly engages with the first and second engaging parts; thus the weight body is firmly fastened to the accommodating section. As a result, a golf club with the required large moment of inertia and low center of gravity is obtainable at a low cost. In addition, since the weight body is press-fitted in the accommodating section with the spacer in between, the spacer is interposed between the weight body and the accommodating section without any gaps. Accordingly, the style of the club head in terms of external appearance is not deteriorated.
It is desirable that the first engaging part be in the form of a groove or undercut which is provided in the inner circumferential portion of the accommodating section of the club head and that the second engaging part be in the form of a groove or recess which is formed in the outer circumferential portion of the weight body. With this structure, the spacer can securely engage with the first and second engaging parts.
It is preferable that the spacer be formed from a material which has an elongation of 10% or greater. With this selection of the material, portions of the spacer can be easily entered in the first and second engaging parts, and the press-fitting force applied to the weight body can be reduced. Thus, an easier mounting of the weight body to the accommodating section can be accomplished. In addition, with an employment of such a spacer, a pressing machine which is not a high-capacity type can be used in the manufacture of the club head of the present invention, and the productive facilities can be simplified.
In the description of the present specification, the term xe2x80x9celongation of the spacerxe2x80x9d generally refers to the breaking elongation measured using the tensile test method for metal materials specified in JISZ 2241 in the range of 5xc2x0 C. to 35xc2x0 C. (20xc2x0 C.xc2x12xc2x0 C. in the case of metals sensitive to temperature changes).